Development of fiber optic biosensors for the detection of numerous biomolecules is proposed. Several novel classes of fiber sensors are detailed. The first is a fiber optic-based ammonia gas sensor which promises to be faster responding with lower limits of detection in comparison to conventional electrode-based ammonia sensors. The preparation of biosensors based on the immobilization of an appropriate enzyme onto the sensing tip of this fiber optic gas sensor is proposed. A new type of biosensor is proposed in which a dehydrogenase is covalently attached to the etched tip of a fused silica optical fiber. A test system which uses the immobilization of fluorescein on etched glass optical fibers is proposed to establish the feasibility of this type of proposed biosensor, and to determine suitable procedures for effective immobilization of reagents on optical fiber tips. Lastly, "internal-enzyme" biosensors are proposed wherein a biocatalyst is immobilized behind a gas-permeable membrane for the detection of volatile bioanalytes. An internal-enzyme biosensor for ethanol will be prepared and evaluated by using alcohol dehydrogenase, nicotinamide adenine dinucliotide, and semicarbazide as the active ingredient in the internal solution.